1. Field of the Invention
The present invention relates to a plasma processing method and, particularly to a plasma processing method which can perform microfabricated or microfabrication plasma processing while replacing gas during the plasma processing.
2. Description of the Related Art
Due to the miniaturization of semiconductor technology and the complication of structure in recent years, vertical profile with a high aspect ratio has been required for an etching process in semiconductor microfabrication. To achieve this, various methods have been known. One of them employs cycle etching to progress etching by alternately repeating two or more processes. For example, there is a method for progressing etching by alternately repeating etching and protection film forming.
Each process constituting the cycle etching has set values of gas type, gas flow rate, pressure in a process chamber, radio-frequency power supplied to an electrode substrate, and the like. To enhance the effects of the gas in each process, the supply timing of the gas, used in each process, and the radio-frequency power, supplied to the electrode substrate for generating bias, should be synchronized.
An amount of the gas introduced into the process chamber is controlled generally by giving a control signal to a mass flow controller (hereinafter, referred to as an MFC) to flow a desired flow rate. However, a delay of approximately one second occurs to introduce the gas into the process chamber after the signal of the flow rate is given to the MFC due to a response time of MFC, pressure, gas flow and the like in a gas piping, shower plates and the process chamber. Moreover, this delay varies about 0.2 to 0.3 seconds.
Thus, if a time for applying the radio-frequency power to the electrode is not controlled in consideration of the delay that the gas is actually introduced to the process chamber after the control signal is given to the MFC, a non-negligible time lag occurs between the timing of generating plasma for performing etching or protection film forming in the process chamber and the timing of generating a bias suitable for each process. This makes it impossible to achieve the optimum processes.
As a method for synchronizing supply timing of the gas and the radio-frequency power applied to the electrode substrate for generating bias, a method for synchronizing the radio-frequency power by determining a replacing time of an etching gas and a protection film forming gas by using an emission spectrum/mass spectrometer to detect the gas concentration is disclosed in JP-2013-58749-A.